Diferratricarbaboranes of the subcloso-[(eta5-C5H5)2Fe2C3B8H11] type, the first representatives of the 13-vertex dimetallatricarbaborane series

Treatment of the [2-Cp-9-tBuNH-closo-2,1,7,9-FeC(3)B(8)H(10)] (1) ferratricarbollide (Cp = eta(5)-C(5)H(5) (-)) with Na(+) C(10)H(8) (-) in 1,2-dimethoxyethane (DME) at room temperature produced an air-sensitive transient anion with a tentatively identified nido-[tBuNH-CpFeC(3)B(8)H(10)](2-) constitution. In-situ reaction of this low-stability ion with [CpFe(CO)(2)I] or [CpFe(CO)(2)](2) generated three violet diferratricarbaboranes identified as paramagnetic subcloso complexes [4,5-Cp(2-)-4,5,1,6,7-Fe(2)C(3)B(8)H(11)] (2; yield 2 %), [4,5-Cp(2-)-4,5,1,7,12-Fe(2)C(3)B(8)H(11)] (3; yield 2 %), and [7-tBuNH-4,5-Cp(2-)-4,5,1,7,12-Fe(2)C(3)B(8)H(10)] (4; yield 14 %). These first representatives of the 13-vertex dimetallatricarbaborane family were characterized by EPR and IR spectroscopy, and mass spectrometry, and their structures were determined by X-ray diffraction analysis.     

Beiträge zur qualitativen „Test Tube“-Papierchromatographie

Zusammenfassung Bei der Trennung und Bestimmung verschiedener reiner Aminosäuren wurde die in vieler Hinsicht einfachere und raschere Test Tube-Methodik näher studiert. Zum Lösen der Aminosäuren erwies sich Ameisensäure als besonders günstig. Bezüglich des Trennungseffektes haben sich als Eintauchmittel besonders eine Mischung von n-Propanol-Wasser und bestimmte ternäre Gemische von tert. Butanol-Methyläthylketon-Wasser und tert. Butanol-Methanol-Wasser bewährt. Außerdem wurde festgestellt, daß die Test Tube-Papierchromatographie besonders auch bei höheren Temperaturen verwendbar ist und hier bessere und raschere Trennungseffekte erzielt werden können. Die Fehlerquellen bei der Bestimmung derR _f Werte wurden eingehend geprüft und dieR _f Werte von 19 Aminosäuren bei verschiedenen Bedingungen in Tabellen angegeben.

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Summary A closer study of the Test Tube Method, which is simpler and faster, was made in the separation and determination of various amino acids. Formic acid was found to be especially good for dissolving the amino acids. With respect to the separation effect, it was found that a mixture of n-propanolwater and certain ternary mixtures of tertiary butanol -methylethylketone-water and tertiary butanol-methanol-water are good as immersion agents. It was also shown that the Test Tube paper chromatography is also applicable at higher temperatures and gives better and more rapid separation effects. The sources of error in the determination of theR _f values were investigated closely and a table is included showing theR _f values of 19 amino acids under various conditions.

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Résumé On a approfondi l'étude de la «technique du tube à essais» dont l'emploi pour la séparation et le dosage de différents amino-acides purs est des plus simples et des plus rapides à de multiples points de vue. Il est apparu que l'acide formique était un solvant particulièrement approprié pour les aminoacides. En ce qui concerne l'effet de séparation, on a obtenu d'excellents résultats par immersion dans un mélange de propanol normal et d'eau ou dans des mélanges ternaires définis de butanol tertiaire, de méthyléthylcétone et d'eau ou de butanol tertiaire, de méthanol et d'eau. On a, en outre, établi que la chromatographie sur papier par la méthode du «tube à essais» est également utilisable lorsqu'on élève la température et qu'elle permet alors d'obtenir des effets de séparation meilleurs et plus rapides. Les sources d'erreurs de la détermination des valeurs deR _f ont été étudiées en détail; un tableau fournit les valeurs deR _f relatives à 19 aminoacides dans des conditions diverses.

     

Rhodium(I) catalysis of cycloprop[a]acenaphthylene isomerizations

Cycloprop [a] acenaphthylene was found to rearrange to phenalene in the presence of rhodium dicarbonyl chloride dimer. Deuterium labeling of this molecule at C(7) (both exo and endo), at C(8), at C(7) (exo) and C(8) and at C(7) (exo), C(8), and C(8') indicated that the C(7) (exo) deuterium was migrating stereospecifically. Furthermore, all of the isotopic label present in the cycloprop[a]acenaphthylene was found statistically distributed over positions 1, 3, 4, 6, 7, and 9 of the phenalene product. Control experiments established the need of the catalyst, the inability to achieve rearrangement of the exo-7-methyl derivative, and the susceptibility of a monodeuterated phenalene for extensive isotopic scrambling in its own right when exposed to rhodium(I). These results have been interpreted on the basis of oxidative addition by rhodium(I) into the central bond of cycloprop[a]acenaphthylene from above the “flap”, followed by shifting of the C(7) (exo) hydrogen (or deuterium) to give a η³-allylrhodim-(III) complex. The experimental data further support a mechanism involving subsequent rearrangement of this intermediate around the periphery of the phenalene ring. This process which is otherwise degenerate is thought to be facilitated by the special electronic features of the phenalenyl system.     

On the symmetric travelling salesman problem I: Inequalities

We investigate several classes of inequalities for the symmetric travelling salesman problem with respect to their facet-defining properties for the associated polytope. A new class of inequalities called comb inequalities is derived and their number shown to grow much faster with the number of cities than the exponentially growing number of subtour-elimination constraints. The dimension of the travelling salesman polytope is calculated and several inequalities are shown to define facets of the polytope. In part II (On the travelling salesman problem II: Lifting theorems and facets) we prove that all subtour-elimination and all comb inequalities define facets of the symmetric travelling salesman polytope.     

The complete figure for second order multiple integral problems in the calculus of variations

Notation Throughout this paper Greek indices, , , and Latin indicesi, j, h, k, assume the values 1, ,m, and 1, ,n respectively. The summation convention is operative in respect of both sets of indices.This work was supported by the South African Council for Scientific and Industrial Research.At time of writing Professor Grässer was Visiting Scholar at the University of Arizona, Tucson, Arizona.     

Notes on planar semimodular lattices. VI. On the structure theorem of planar semimodular lattices

In a recent paper, G. Czédli and E. T. Schmidt present a structure theorem for planar semimodular lattices. In this note, we present an alternative proof.     

Facile Phenylphosphinidene Transfer Reactions from Carbene–Phosphinidene Zinc Complexes

Phosphinidenes [R-P] are convenient P₁ building blocks for the synthesis of a plethora of organophosphorus compounds. Thus far, transition-metal-complexed phosphinidenes have been used for their singlet ground-state reactivity to promote selective addition and insertion reactions. One disadvantage of this approach is that after transfer of the P₁ moiety to the substrate, a challenging demetallation step is required to provide the free phosphine. We report a simple method that enables the Lewis acid promoted transfer of phenylphosphinidene, [PhP], from NHC=PPh adducts (NHC=N-heterocyclic carbene) to various substrates to produce directly uncoordinated phosphorus heterocycles that are difficult to obtain otherwise.     

From Low- to High-Dimensional Moments Without Magic

We aim to compute the first few moments of a high-dimensional random vector from the first few moments of a number of its low-dimensional projections. To this end, we identify algebraic conditions on the set of low-dimensional projectors that yield explicit reconstruction formulas. We also provide a computational framework, with which suitable projectors can be derived by solving an optimization problem. Finally, we show that randomized projections permit approximate recovery.     

The Mystery of Gabor Frames

This is a survey about the theory of Gabor frames. We review the structural results about Gabor frames over a lattice and then discuss the few known results about the fine structure of Gabor frames. We add a new result about the relation between properties of the window and properties of the frame set and conclude with a vision of how a more complete theory of the fine structure might look like.